John the Ripper is a UNIX password cracker, currently available for UNIX
(tested with Linux x86, FreeBSD x86, Solaris 2.x SPARC, OSF/1 Alpha), DOS,
WinNT/Win95.

    John the Ripper supports the following cracking modes:
    - wordlist with or without rules;
    - "single crack", makes use of the login/GECOS information;
    - incremental, tries all character combinations;
    - external, allows you to define your own cracking mode.
    - MD5 based password files support

WWW: http://www.openwall.com/john/